This invention relates to apparatus for heat-treating a liquid product, which product is temporarily subjected to a high temperature, comprising series-connected multi-tube heat exchangers, a heating-up heat exchanger, a high-temperature heat-exchanger and a cooling-down heat-exchanger, the heating-up and cooling-down heat-exchangers being interconnected by means of a pipe system for regenerative heat-exchange, the apparatus being connected to conduits for supplying and/or discharging heat and being provided with measuring, monitoring and control equipment.
Apparatus of this kind is frequently used for sterilizing fruit juices, milk products and milk. On the one hand, the product to be treated has to be kept at a high temperature for a certain time during the treatment, in order to ensure that contaminating organisms are rendered sufficiently inactive, while on the other hand the time during which the product is kept at high temperature must not be too long since otherwise undesirable changes in the quality and the taste of the product are caused. This applies particularly to milk and milk products. Good results are obtained by heating the product for a short time to the required high heating temperature and keeping it at that temperature for an accurately maintained short period, and then cooling it rapidly.
EP-A No. 0 036 124 discloses an apparatus of this kind. This apparatus is constructed from a large number of identical tube heat-exchanger sections which are assembled to form heat-exchangers in which the product is respectively preheated, heated and cooled. Each tube heat-exchanger section consists of a tubular housing accommodating a number of parallel tubes mounted in the housing by means of two end plates. The product to be treated flows from the common space in front of one end plate to the common space behind the other end plate via the tubes. A heating and coolling fluid respectively flows in the housing between the two end plates. This means that the product to be treated is divided into separate flows in each heat-exchanger section for takingup and yielding heat respectively and that these flows are combined again at the end of each heat-exchanger section, whereupon the product is fed via a connecting pipe to the next heat-exchanger section, where it is again divided and so on.
Consequently, the connecting pipes are always at the average temperature and it is impossible to check whether one or more tubes of a certain heat exchanger are fouled. When the apparatus is washed out with a cleaning agent it will also be impossible to tell whether the tubes with the most fouling have been fully cleaned. One of the results of this may be that blockages still present locally will prevent some of the cleaning liquid from being removed, so that this liquid may mix with the product during the subsequent heat-treatment. The remaining fouling also causes a reduction in the sterilizing efficiency of the apparatus and accelerated new fouling, so that the cleaning frequency has to be increased at the expense of heat-treatment operating time. There is also the risk that the product will be inadequately heated in some of the tubes so that not all the bacteria are destroyed, and this inadequately treated product may again be mixed with product which has been subjected to the correct treatment.